I. Field of the Invention
This invention relates to the field of communications systems and, in particular, to the transmission of message signals in a communications system.
II. Description of the Prior Art
In mobile radio communication systems, signals containing message information are transmitted for reception by a plurality of receivers. The signals are transmitted by way of communication channels wherein fading can occur. The fading in the communications channels can cause interference with the received signal and can degrade the received signal, thereby causing message information in the signal to be lost. Furthermore, other transmitting sources of varying power level usually exist and create noise at a receiver. Examples of other noise sources include signals from the same transmitter, signals from other transmitters or signals from different devices such as electric motors, televisions or compact disk players.
Successful recovery of transmitted information is a function of the ratio of the power of the received signal containing the information to the power of the received noise. An indication of the amount of noise that occurs during reception can therefore significantly improve the recovery of information from a received signal. For example, a Turbo decoder which relies on an accurate knowledge of the noise power at the receiver, can be used to improve recovery of information from a received signal. An indication of the amount of noise that occurs during reception can also be used to control the transmit power of the signal, so as to maintain the received signal to noise power at an appropriate level.
The present invention is directed to a method and apparatus for improving the transmission of an information signal having message information. A received information signal is formed from an information signal transmitted through an information channel. The received information signal has signal noise. The message information is removed from the received information signal to provide a symbol sequence that is then applied to a first filter to provide a first filtered signal. The power of the first filtered signal is determined and applied to a second filter to provide a second filtered signal representative of the signal noise of the received information signal.